# Geographic Functions

Geographical functions operate on geographic input, like points, lines or polygons. The built-in general-purpose geographic functions are listed in below.

## Geography functions​

FunctionDescription
`geo_make_point(latitude double, longitude double)``geography(point)`Creates a point with coordinates `latitude` and `longitude`
`geo_make_line(a geography(point), b geography(point))``geography(linestring)`Creates a line between `a` and `b`
`geo_distance(a geography(point),b geography (point), unit string)``double`Distance in the WGS84 ellipsoid between points `a` and `b` expressed in `unit`
`geo_buffer(p geography(point), r double, unit string)``geography(polygon)`120-sided polygon around point `p`, which is fully enclosed by circle with center in same point and radius `r`, where radius unit is given in `unit`. When radius is 0, a single point is returned (the input parameter) instead of a 120-sided polygon
`geo_auto_vertex_order(arg geography)``geography`Inverts the vertex order for all polygons if they are specified in an interior-right winding order assuming flat earth to topology 4
`geo_invert_vertex_order(arg geography)``geography`Inverts the vertex order of all polygons
note

Explicit use of `geo_auto_vertex_order` is needed and recommended only when processing extracts generated by Hyper API version v0.0.12514 or earlier. `geo_auto_vertex_order` is implicitly used when parsing `GEOGRAPHY` values from WKT format.

### Examples​

To pass a `geography` constant as an argument, it needs to be cast from a string which contains a `geography` object formatted in the Well Known Text (WKT) format defined by the Open GIS Consortium, Inc, in the OpenGIS Simple Features Specification For SQL. More examples of handling `geography` objects using the Hyper API can be found here. Return values of type `geography` are also shown in WKT format.

``SELECT geo_make_point(20, 30);Result: point(30.0000003 20.0)(Note that the latitude and longitude are flipped in the result, because it is shown in the WKT format as point(longitude latitude).)SELECT geo_make_line('point(14 42)'::geography,'point(18 43)'::geography);Result: linestring(14.0000003 42.0000002, 18.0000003 43.0000001)SELECT geo_distance('point(0 0)'::geography, 'point(0 1)'::geography, 'kilometers');Result: 110.574372592802SELECT geo_buffer('point(90 45)'::geography, 1989.0, 'meter');Result: polygon((90.0000002 45.0178973, 89.9986795 45.0178727, ..., 90.0013209 45.0178727, 90.0000002 45.0178973))SELECT geo_invert_vertex_order('geometrycollection(polygon((0 0, 2 0, 0 4, 0 0)), polygon((0 0, 0 2, 4 0, 0 0)), point(0 2))'::geography);Result: geometry collection(polygon((0.0 0.0,0.0 4.0,2.0000003 0.0,0.0 0.0)), polygon((0.0 0.0,4.0 0.0,0.0 2.0000003,0.0 0.0)), point(0.0 2.0000003))SELECT geo_auto_vertex_order('geometrycollection(polygon((0 0, 2 0, 0 4, 0 0)), polygon((0 0, 0 2, 4 0, 0 0)), point(0 2))'::geography);Result: geometrycollection(polygon((0.0 0.0,2.0000003 0.0,0.0 4.0,0.0 0.0)), polygon((0.0 0.0,4.0 0.0,0.0 2.0000003,0.0 0.0)),point(0.0 2.0000003))``

## Supported distance units​

The supported units of length are:

Unit name in American spellingOther supported spellingsDescription
metermetre, m, meters, metresBase unit of length in International System of Units (SI)
kilometerkilometre, km, kilometers, kilometresEqual to 1000 meters
milemi, milesEqual to 1609.344 meters
footft, feetEqual to 0.3048 meters